2. Field of the Invention
The present invention is related to single reel cartridges for magnetic tape and, in particular, to such a cartridge in which a leader block is attached to the free end of the tape to seal the cartridge when not in use and provide positive connection for automatic threading.
3. Description of the Related Art
There are many known types of single reel cartridges for magnetic tape and photographic film. One type of cartridge which is used with magnetic tape is disclosed in U.S. Pat. Nos. 4,383,660; 4,426,047; and 4,452,406. The cartridge disclosed in these patents has a structure similar to that of cartridge 10 in FIG. 1. A reel 12 of tape 14 is contained by first and second casing members 16 and 18 which are joined together by cementing or other means. The free end 14a of the tape 14 is secured to a leader block 20 by a pin 22 inserted in a slotted hole 24. The leading 26 and trailing 28 surfaces of the leader block 20 are removably secured between edges 30 and 32 of the side walls 34 and 36, respectively, of the second casing 18. The edges 30 and 32 partially define an outer aperture 37 of a receiving well 38 through which the leader block 20 passes when it is removed from the cartridge 10. The leader block 20 has a shape which permits an auto-threading device to engage the leader block 20, permitting the leader block 20 to be removed from the receiving well 38 and inserted into the hub of a takeup spool (not shown) so that the tape 14 can be smoothly wound over the trailing edge 28. These features of the leader block 20 are disclosed in U.S. Pat. Nos. 4,426,047 and 4,452,406.
A spring 40, secured by projection 42, forces a brake plate 44 against the reel 12 so that the outer surface of hub 46 fills the central aperture 48 in the first casing member 16 and a brake button 50 protrudes through the center of the hub 46; thus, substantially sealing the planar surface of the first casing member 16. As a result, the tape 14 is substantially completely enclosed by the cartridge 10 and leader block 20 when the receiving well 38 is filled by the leader blck 20, as illustrated by the solid line position of leader block 20 in FIG. 2.
The conventional construction of the cartridge illustrated in FIG. 1 is described in further detail in the above-mentioned U.S. Patents, particularly U.S. Pat. No. 4,383,660, incorporated herein by reference. However, these patents do not disclose the susceptibility of such a cartridge to a problem that is common with all single reel tape cartridges which have a free end. This problem, as described in column 1, lines 39-47 of U.S. Pat. No. 3,682,415, is the tendency of such cartridges to unwind due to the leader (free end 14a) becoming unsecured and falling into the enclosing cartridge. Although the leader block 20 provides a better than usual solution to this problem, conventional cartridges constructed as disclosed in U.S. Pat. No. 4,383,660 have been known to have the leader block 20 driven into the interior of the cartridge 10 by an external force. Due to the construction of these cartridges, it is extremely difficult to retrieve the leader block 20 from the interior of the cartridge 10 without damaging one or both of the casing members 16 and 18.